1. Field of the Invention
This invention relates to a system or means for connecting tubular shaped conductors to other conductors, particularly for use in electrical power supply lines.
2. Summary of the Prior Art
In the power supply and transmission industry, there are many applications where conductors, or sections of conductor are provided with a hollow cylindrical tube, for example a rigid tube in copper or aluminum, for connection to a clamping connector. For certain applications, tube conductors may have a number of mechanical and electrical advantages. For example, in proportion to their mass, they have good electrical current transmission properties due to "skin effect", whereby electrical current intensity tends to be greater proximate the surface of a conductor than within the core. There may be other advantages, for example tube conductors have larger contact surfaces than solid conductors (i.e. there diameter is greater for a given conductor cross-sectional area). Tube conductors can also be used at their ends to receive other conductors therein, the tube conductor being crimped to the inner conductor for interconnection purposes. The tube conductor may also provide a lightweight rigid interconnection means between electrical connectors or devices located in proximity with each other.
One of the problems with tube conductors is the difficulty of connecting the conductor to a connector, and maintaining a reliable connection over the lifetime of the connector. For example, in the electrical power industry it is typical to use clamping connectors that comprise bolts for clamping down on a conductor inserted in the connector. When using a tube conductor, it is typical to crush the tube during the clamping with a bolt, in order to provide the required contact force to ensure good electrical connection. Deformation of the tube may be disadvantageous if it is important to maintain the cylindrical shape of the tube conductor in a region proximate the connector. Furthermore, the large deformation displacement entails greater unreliability in the quality of the crushed conductor, contrary to a solid conductor which can be supported around the whole periphery such that maximum contact surface area and pressure is obtained. Upon thermal and mechanical stresses, a crushed tube conductor may relax and as a consequence contact forces are reduced and the performance of the connection is impaired. Another problem in the power industry is to interconnect different metals, for example aluminum alloys to other conductors such as copper, brass or steel. One of the problems stems from the different thermal expansion coefficients of different metals. Differing expansions of metals held fairly rigidly together in the contact region may cause plastic deformation thereof, leading to a relaxation of contact pressure between the contacts. It is also particularly problematic to connect aluminum to another conductor by a clamping conductor, because of the stress relaxation properties of aluminum when subject to thermal or mechanical stress cycles. The latter effects pose a problem in the industry as it is often necessary to make the transition from a copper conductor, for example, to an aluminum conductor.